1. Field of the Invention
The invention relates to radar systems generally, and more particularly to systems for generating continuous 360 degree rotation of a beam.
2. Description of the Prior Art
The form of a cylindrical antenna to which the present invention might be applied to variously described in the patent and other technical literature. For example U.S. Pat. No. 3,474,446 describes an array of microwave radiators in vercial columns about a circular perimeter forming a cylinder. Another prior art device is described in U.S. Pat. No. 3,653,057. Both of those patents involve electronic scanning means, and the said U.S. Pat. No. 3,653,057 involves electronic scanning or pointing of a beam about 360 degrees of azimuth.
Electronically-scanned, cylindrical array antennas are advantageous for applications where azimuth scan of the full 360 degrees is required and where the characteristics of the beam must remain substantially unchanged over this full range of azimuth angles.
Electronic scanning of a set of three or more prior art appropriately oriented planar phased arrays can provide wide angle coverage in aximuth but results in beam distortions, (i.e., beam characteristics are not uniform with angle). Morever such arrangements are quite expensive and uneconomical of available space.
Mechanically rotating antennas provide the required beam characteristic but usually do not have the required data rate. Furthermore the prime power requirement is much higher and the life-cycle costs tend to be greater as compared to electronic scanning systems due to the relatively large motor drive and its servicing.
Existing all-electronic cylindrical arrays also have disadvantages. In a practical configuration, they require many active sub-assemblies with an unacceptably large amount of loss and require frequent maintenance to avoid anomalous beam characteristics due to failures among the many components and sub-assemblies. Morever, variations in sub-assembly characteristics, due to component tolerances and differences, may cause variations in the beam characteristics as a function of azimuth angle. Although such variations may be relatively small, they can be important in certain exacting situations.
An existing electro-mechanical commutating feed known in the art as the Wullenweber Cylindrical Array Feed has the desired low drive power and high reliability since it uses a low-inertia mechanically rotating feed. In that design, however, power is capacitively coupled from rotor to stator transmission lines which in turn connect to the larger cylindrical array elements. It is known that such capacitive coupling causes a relatively large power loss and flutter or fluctuations in the radiated beam with rotational angle.
The manner in which the present invention incorporates the mechanical advantages of the Wullenweber device while greatly improving upon its power transfer and flutter characteristics will be seen as this description proceeds.